Automatic volume control arrangement



Oct. 29, 1935.

L. E. BARTON AUTOMATIC VOLUME CONTROL ARRANGEMENT Filed Aug. l5, 1933wooo-0000000L #iP/9000657? Hil f/L INVENToR f LOY E. BARTON BY/`.MM

ATTORNEY Patented Oct. 29, 1935 ST Sli.,

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AUTOMATIC VOLUIVIE CONTROL ARRANGEMENT of Delaware Application August15, 1933, Serial No. 685,186

10 Claims.

My present invention relates to radio receivers, and particularly toautomatic volume control arrangements for superheterodyne receiverswhich do not employ intermediate frequency or radio frequency amplifierstages.

Automatic gain control is usually applied tca radio receiver in presentday receiver construction by regulating the bias on a gain controlelectrede of a radio frequency or intermediate frequency amplifier.There are receiver constructions employed where radio frequencyamplifier and intermediate frequency amplier stages are dispensed with.For example, such constructions are usually employed where compactnessand economy of construction are prime considerations. An automobileradio receiver is an illustration of such a compact receiver.

In the case of such compact radio receivers the regulation of the highfrequency amplifier bias for gain control is preferably replaced by anautomatic control of the signal energy transfer between the signalcollecting means and the radio receiver. Of course, to preserve thecompactness consideration, it is necessary to` utilize this latter typeof control without the addition of auxiliary elements which only serveto increase the cost of production and assembly.

Accordingly, it may be stated that it is one of the primary objects ofthe present invention to provide a radio receiver of the typeA whereinno high frequency amplification is employed between the signalcollecting means and the detector, and wherein automatic volume controlis accomplished by regulating the transfer of energy between the signalcollecting means and the detector, this regulation being accomplishedwith a minimum of circuit elements.

Another important object of the present invention is to provide asuperheterodyne receiver employing no radio frequency or intermediatefrequency amplifiers, and wherein the second detector stage is utilizedto control automatically the transfer of signal energy between thesignal collecting means and the rst detector.

Another object of the invention is to provide a superheterodyne receiverutilizing between the antenna and the audio frequency network solely acombined oscillator detector and a second detector in cascade, thesecond detector being of the duplek diode triode type and one of thediodes of the second ldetector being utilized to automatically regulatethe transfer of signal energy between the antenna and the combinedoscillator detector.

Still other objects of the invention are to improve generally thesimplicity and eiciency of automatic volume control arrangements forsuperheterodyne receivers, and to especially provide an automatic Volumecontrol system which is not only simple and eiiicient in operation, buteconomically manufactured and assembled in a com- '-5 pact type of radioreceiver.

The novel features which I believe to be characteristic of my inventionare set forth in the appended claims, the invention itself, however, asto both its organization and method of operation l0 will best beunderstood by reference to the following description taken in connectionwith the drawing in which I have indicated diagrammatically one circuitarrangement whereby my invention may be carried intol effect.

In the drawing there is shown a conventional radio receiver of thesuperheterodyne type between the signal collecting means and the audiofrequency network of which solely a frequency changer stage and a seconddetector stage in cas- 20 cade are employed. The signal collecting meansis illustrated in the drawing by the usual grounded antenna circuit A,this circuit including a resistor R1 having one side thereof connectedto an intermediate point of a coil l, one side of the 25 coil beinggrounded. The intermediate tap to this coil divides the coil into twoportions L1 and L2. The coil portion L1 is magnetically coupled, as atM1to the coil L3 of the tunable selector circuit 2 of the frequencychanger network 3. 30 The coil portions L2 and L3 are magneticallycoupled. The network 3 is preferably of the combined oscillator detectortype well known to those skilled in the art.

Of course, the network 3 can be composed of 35 the equally well knownindependent first detector and local oscillator circuits, but for thesake of compactness it is preferable to use a combined oscillatordetector stage. In that case the circuit 2 is to be considered as thesignal frequency input 40 circuit of the oscillator-detector, while thecircuit 4 is to be considered as the local oscillation frequencyresonant circuit. The numerals 5 and 6 respectively designate thevariable tuning condensers in the signal and local oscillation circuits,4 and a dotted line l is shown to represent a. mechanical uni-controldevice, of any well known form, for adjusting the variable condensers 5and 6.

rl'he circuit 8, in the output of the network 3, 50 is resonant to theoperating intermediate frequency and is coupled, as at M2, to a network9 also resonant to the intermediate frequency. The specic circuitelements of the network 3 are not shown for the reason that the combinedoscil- 55 lator detector stage details are not a part of the presentinvention. However, reference is made to application Serial No. 654,421,iiled January 31, 1933 by J. C. Smith for a disclosure of a pentagridoscillator converter circuit which may be employed in the network 3. Thetube employed in such a network is of the type known as a 2A7, thoseskilled in the art being well aware of its construction.

The intermediate frequency energy acrossjthe circuit 9 is impressed upona diode rectifier circuit. The diode rectifier circuit functions as thesecond detector, a tube I0, known as a 'duplex diode triode, beingutilized inthe second detector stage. This tubelisV commerciallyjknownas a 55 type tube, and its physical construction has been disclosed in aco-pending application of T. M. Shrader, application Serial Nos-"622,140filed July 12, 1932. The tube I Il includes can indirectly heatedcathode, the cathode being commom-forthe diodeanode elements' II andI2,V and for rthe triode grid and plate I 3 and I4. Ihe diode elementsII and I2 are disposed around an extreme portion '.of the cathodesleeve. The diodesfunction independently of each other and of the triodesection of the tube Ill. The electron stream flowing towards the grid I3and the plate 'I4 isllin'depen'dent of the-electronfstream flowingtowards the diode anode II and the diode anode I2. The high potentialside of circuit 9 is connected to the diode anode II, while the low p0-tential side is connected to the common cathode "sleeve lead through acondenser I 5, the condenser being shunted by aresistor I6.

The diode anode I2 is connected by a lead Il `to the ungrounded side ofcoil I, and this lead has been designated A. V. C.. As will be pointedout hereinafter in detail, the lead I'l constitutes `the volumeregulation patnfor the -receiver. Positivewpotentialliseappliedtothe-platel I4 of tubef IIJ-from a source B (not shown), the plateIII-being connected to thepositive terminal of source B through a; pathwhich includes the lead IB-and the'audiofrequencychoke I9. The grid VI3of tube I0 vis connectedby a lead 2B toone `side of the resistor I6,through resistor IEa, and Aitwill be understood that there is impressedon the .gridA I3 the audio frequency component of the Yrectifiedintermediate frequency energy, which' component ilowsin the circuitconnected to the diode anode II and the commoncathode lead of tube. I.Resistor ISa attenuates any I. F. voltage across I5 and IB.

The triode section, including the `common cathode,` the grid I3 andplate I4, functions as ,an amplifier of the audio frequency component ofthe rectified intermediate frequency energy, andthis amplified ,audioenergy is ,transferredV to `a succeeding .audio frequency amplifier 2l`through an. adjustable path whichV includes the direct currentblockingcondenser 22 andthe manuallyradjustable.resistor.23. v'Ilfie output ofthe network 2 I, ,mayV then beimpressed `uponany suitabletype ofreproducer, such l as an electrodynamic` loud speaker. --It is alsopossible .to kimpress the output of tube I0 upon the reproducer "withoutfurtherfamplication.

The field coil 24 of the-reproducer has one side thereof connected'tothe negative terminal of the sourceqBf whilev its. otherI side isgrounded. The common-cathode sleevefleadof tube' I Il'isconnectedfto1agpoint-on the coilf24 such that the ground 1 side of,thefcoil124-is at-abouti25 volts with respect yto'thespoint on coil 24to which'the resistorRz is connected. This potential diiference isdesignated by the symbol E1. A radio frequency bypass condenser 25 isconnected between the grounded side of the eld coil 24 and the commoncathode sleeve lead of tube l0, the con- 5 denser 25 being connected inshunt with the resistor R2. An audio frequency by-pass condenser 26 isconnected between the ungrounded side of condenser 25 and the potentialsupply source side of choke coil I9.

The magnitude of the resistor R2 is so chosen that the potentialdifference E2 in the absence ofreceived signal energy is about 35 volts.Of

course, the values for E2 and E1 are purely illustrative, and are notgiven by way of limitation. l

The potentialsEz .and E1 function to provide a delay of the automaticvolume control action :until, ;a predetermined signal intensity levelhas been attained. In general, the automatic volume control action willnot commence until the poten- 2 tial E2 has become .approximately equalto or less` tha-n-thepotentialE1. This type of delayed automaticvolumecontrol-y arrangement has been disclosedby me in connection with asecond vdetector of the 55 type in my copending application SerialNo.-640,94'6, filed Novemberi3, 1932.

lead Il and coil I, and therefore with no signal energy'being received:the diode anode I2 is at a negativepotential -with respect to thecathode of tube IU. 'This necessarily followslfrom the 4 fact-that withno signal energy coming in the value'Ez is greater than the value E1.Since the diode anode I2 is negative with respect to the fcathode; thisVdiode circuit is non-conductive.

"As soon as signal -energy is collected by the 4 vantenna-:circuit A,and intermediate frequency energy is impressed upon circuit-Sl, thereisrim- -,pressed uponthe grid I3 rectified :energy poten- 'tialresulting from'the potential dropv across resistorl` in the 'diodedetector circuit including 5 dio'defanode` II. kThegrid I3 thereforebecomes :more negative arid-*the =plate=current flow-inthe triodesection of tube!! decreases with the result that the value-E2 approachesthe value E1. `That `is to say, the cathode side of resistor R2 ap'proaches in `pot'e'ntialvalue the ground-side -of field coil 24. l

'It-will" therefore be seen that until thevalue E2 actually becomes veryclose to (about 0.5 volts negative) Cthe value'E1, the diode Vanode I2will 6 vbe sucientlyjnegative with respect'to the cathoder-of tube IG,to prevent current-*now to the diode. As soon as that signal intensitylevel has been attained which results in Ez becoming suiiiciently'lowwith respect to E1, the diode ,circuit 6 Awhich includes the diodefanodeI2 becomes con- Vvductive.

Y-This conductivity xresults in a ilow of radio frequency energythrougha path which includes the coil portion L2, the lead Il, the diode anodeI 2,the common cathode of tube IE), the radio 'frequency'by-passcondenser 25, and back to ground to the coil portion L1. It will b eobserved lthat this'flow of 'signal energy is'in a direction opposite tothe flow of signal energyY through the 75 nected toyground through thepath including l coil portion L1. In other Words, as soon as the controldiode becomes conductive there is induced in the coil L3 a voltage whichis proportional to the voltage across L1, minus the voltage across L2.

Obviously, as the signal intensity level rises more and more energy isdiverted through the coil L2, because of a lower effective resistance ofthe diode circuit, and the relative amount of signal energy reaching theinput circuit 2 is re-' duced. In this way the transfer of energy fromthe signal collecting means to the frequency* changer network 3 isautomatically regulated, and in dependence on the variation in amplitudeof the received carrier energy, in such a manner that the carrier energyinput to the circuit 9 is maintained substantially constant.

The control diode .may also be employed as a Short circuiting resistanceacross the antenna coil l without the utilization of the aforo-describedbucking action. This arrangement is obvious, and need not be describedin any further' detail. It is also possible to apply this general schemeacross circuit 2 and other circuits in the receiver for automatic volumecontrol purposes, which may also be so arranged that automaticselectivity may be obtained. It is obvious that the A. V. C. diode maybe a separate diode tube in which the cathode is connected to thecathode of tube lll. It is also possible that a separatel diode tube maybe necessary instead of a common tube to prevent undue signal feedback.The resistance Ri is largecompared to the average antenna impedance,usually about 1000 ohms, so that different antennas cause less variationof signal to L1 and also to permit poorer regulation of antenna voltagewhich adds to the effectiveness of the A. V. C. system because theaction of L1 and L2 is to short circuit the antenna to ground.

While I have indicated and described one system for carrying myinvention into effect, it will be apparent to one skilled in the artthat my invention is by no means limited to the particular organizationshown and described, but that many modifications may be made withoutdeparting from the scope of my invention as set forth in the appendedclaims.

What I claim is:

l. In combination, a signal source having parallel paths connected to acommon point of invariable potential in signal bucking relation, a tunedcircuit coupled to said paths, and means controlled by the signalintensity to cause signal current to f'low through one oi said pathsonly when the signal intensity has reached a predetermined level.

2. A signal collecting means having parallel paths connected to a commonpoint of invariable potential in signal bucking relation, one of whichpaths includes an electron discharge device, a tuned circuit coupled tosaid paths, and a rectifier connected to said tuned circuit, and meansconnected to said rectifier and said device whereby the latter isrendered conductive only when the collected signal energy intensityattains a predetermined level.

3. In a superheterodyne receiver of a compact type including between theantenna circuit and audio frequency network solely a combinedoscillator-rst detector and a second detector, an automatic volumecontrol arrangement therefor including a pair of parallel paths in theantenna circuit, at least one of which paths is coupled to saidoscillator-detector to transfer energy thereto, and the other pathincluding a control diode, said control diode being connected to saidsecond detector so that the control diode becomes conductive only whenreceived signal energy exceeds a predetermined intensity level, said 5parallel paths being in signal energy flow opposing relation.

4. In a superheterodyne receiver provided with a rst detector and asecond detector, the latter including a pair of independent diodesections l and a triode section, a tuned circuit coupling the output ofthe first detector and one of said diode sections, a connection betweenthe grid of said triode section and a point on the circuit of said firstdiode section, means for connecting the l second diode section to anantenna circuit coupled to said first detector input, and means in thespace current path of said triode section for maintaining the seconddiode section inoperative to conduct radio frequency ener-gy until apredetermined intensity level of received signal energy is exceeded.

5. In combination, a signal collector, a pair of parallel pathsconnected between the collector and a point of invariable potential insignal bucking relation, a tuned circuit coupled to at least one of saidpaths, a diode rectifier coupled to the tuned circuit, a grid and plateassociated with the diode cathode, at least one of said paths beingconnected to said point through a second diode and an impedance in thespace current path between said plate and cathode, and a connection fromsaid grid to said rectier.

6. In combination, a signal collector, a pair of parallel pathsconnected between the collector and a point of invariable potential insignal bucking relation, a tuned circuit coupled to at least one of saidpaths, a diode rectifier coupled to the tuned circuit, a grid and plateassociated with the diode cathode, at least one of said paths beingconnected to said point through a second diode and an impedance in thespace current path between said plate and cathode, a connection fromsaid grid to said rectier, and a source of direct curr-ent voltageconnected between the said cathode and plate, a second impedance beingconnected from the negative terminal of the voltage source to saidpoint.

7. In combination, a signal collector, a pair of parallel pathsconnected between the collector and a point of invariable potential insignal bucking relation, a tuned circuit coupled to at least one of saidpaths, a diode rectifier coupled to the tuned circuit, a grid an-d plateassociated with the diode cathode, at least one of said paths beingconnected to said point through a second diode and an imp-edance in thespace current path between said plate and cathode, and a connection fromsaid grid to said rectifier, said cathode functioning as the electronsource of the second diode.

8. In combination, a signal collector, a pair of parallel pathsconnected between the collector and a point of invariable potential insignal bucking relation, a tuned circuit coupled to at least one of saidpaths, a diode rectifier coupled to the tuned circuit, a grid and plateassociated with the diode cathode, at least one of said paths beingconnected to said point through a second diode and an impedance in thespace current path between said plate and cathode, a connection fromsaid grid to said rectifier, and common tube envelope housing the twodiodes, grid and plate.

9. In combination, a signal collector, a pair of parallel pathsconnected between the collector and a point of invariable potential, atuned cir- 1 cuit coupled to at least one of. said paths, a dioderectifier' coupled to the tuned circuit, agrid and plate associated withthe 'diode cathode, at least one of said paths being connected to saidpoint through a second diode and an `impedance in the space current pathbetween said plate and cathode, and a fconnection from saidV grid tosaid rectier, said paths being connected in signal phase opposition, andvariations in Voltage drop across the said impedance controlling theconductivity of the seconddiode.

10. In combination With a multiple duty tube including a pair ofdiodesections and an amplicoupled between the anode of one diode sectionand the cathode, a signal collector, a coil having one side thereofconnected to the anode of the A second diode section, the other side ofthe coil being connected to the cathode through an impedance, thecollector being connected to a point on said coil, said tuned circuitbeing coupled to said coil, and a connection from a control electrode insaid amplifier section toa point 'in the circuit of said one diodesection.

LOY E. BARTON.

